Compression Ratio

What is compression ratio?

Here's an example: a compression ratio of 200:1 describes the original video with the numeric value of 200. In comparison, the compressed video is represented by the lower number. As more compression occurs, the numerical difference between the two numbers increases. The compression ratio is equal to the size of the original image divided by the size of the compressed image. Remember the formula (R = C/O) A 10 MB file that compresses to 2 MB would have a 5:1 compression ratio.

Another way to look at it is that MPEG4 video compressed to a 30:1 ratio allows the storage of 30 compressed frames in the same space as a single uncompressed frame.

In most cases, the video quality decreases as the compression ratio increases. This is the obvious result of throwing away more and more information to achieve compression. Think of it in terms of making orange juice from fresh oranges.

From Digital CCTV by Emily M. Harwood.